The invention relates to a method of applying a paint to a shear caulked portion around the outer periphery of a shell as may be used in a brake booster which may be formed by a pair of cylindrical or circular members caulked together.
A shell used for a brake booster generally comprises a cup-shaped or a substantially cylindrical member having a bottom and a circular or dish-shaped member, which are both painted and then dried before assembly. These members are disposed in abutment against each other, and are joined together by caulking them together after a peripheral margin formed by the abutment has been sheared off.
The shear caulked portion includes an exposed metal which is likely to give rise to the occurrence of a rust, and thus requires a painting to prevent such rust. In the prior art practice, a substantially cylindrical shell which is formed by the caulking operation and which is to be painted is disposed so that the axis thereof is disposed at an angle and so that the shell is rotatable about the axis. A vessel containing a quantity of paint which is sufficient to allow the shear caulked portion extending around the outer periphery of the shell to be immersed therein is disposed below the shell, and the painting is applied to the shell while rotating it (see Japanese Laid-open Patent Application No. 242,163/1989). However, applying the paint by immersing the shell in the paint vessel involves a wasteful use of the paint and the run down of the paint, which degrades the appearance, resulting in an inefficient operation and a difficulty to achieve a uniform painting.